that connect the Orders and Families of Birds. 469 
Among the advantages derived from an inspection of the fore- 
going diagram is that of our being able to discern at one view the 
gradual deviation which takes place in the various groups from 
the more typical form and character of the order. If we fix our 
attention steadily on the central and typical group of Conirostres, 
we may trace out at a glance the limits by which that perfect for- 
mation depending upon the more important characters is partially 
preserved, or entirely lost, according as the groups we examine 
are more or less in its vicinity. Let us select, for instance, such 
essential characters as strength and regular construction of the 
bili and foot, the powers of the voice, or the organs of digestion. 
We see the first of these characters, the perfect bill of the Coniros- 
tres, preserved in the neighbouring Scansores, though partially 
superseded by the use of the tongue in the Picide and Certhiade, 
until it is entirely lost in the Tenuirostres, and the typical fami- 
lies of the Fissirostres. We see it again recovered in those aber- 
rant families of that tribe which join the Dentirostres, where the 
perfect form re-appears, though the strength is not equal to that 
found in the typical tribe of the order. The perfect foot again 
may be perceived to become in some measure defective in the 
Scansores, to be entirely lost in the types of the Tenuirostres and 
- Fissirostres, and finally to be resumed as we come round by the 
Dentirostres to the tribe from which we set out. We may again 
mark out, on examining this diagram, how far the more perfect 
powers of voice that distinguish the typical groups of the Coniros- 
tres, are communicated to the neighbouring families on each side ; 
such as the Psittacide among the Scansores, the Merulide and Syl- 
viade among the Dentirostres; but how completely they are lost in 
the remoter families. The same observation may be made re- 
specting the more extensive powers of digestion which distinguish 
the omnivorous families of the same typical tribe. These powers 
are perceived to be singularly deficient in the remote groups of 
3»2 the 
